Embodiments of the invention relate to the field of position determination, in particular a position sensor for the determination of the state of deflection of a movably arranged mechanical component.
According to conventional technology, different categories of position sensors for determining the deflection state of a mechanical component are known. Discretely assembled optical or electric/magnetic sensors, but also integrated sensors are known.
Incremental encoders are part of the category of discretely assembled optical or electric/magnetic position sensors. The same are used both for translationally and also for rotationally movably arranged mechanical components. The functioning of incremental encoders is based on an exact scanning of optical or magnetic scales. Depending on the assembly and implementation, position sensors based on incremental encoders are able to determine the position or the deflection state of a mechanical component very accurately, however they need a comparatively large design space. For this reason, incremental encoders are mainly used in macroscopic devices, like, e.g., in turntables and positioning tables. For use in miniaturized systems, in particular for use in endoscopic applications, position sensors based on incremental encoders are not suitable, however.
For small mechanical components, like, e.g., for microscanner mirrors, further discretely assembled optical devices are known, so-called free beam arrangements. In a free beam arrangement, the measurement of the deflection state of a movably arranged mechanical component is generally executed with the help of a laser beam. The laser beam is directed at the mechanical component and reflected or deflected by the mechanical component, depending on the current deflection of the component, in different directions. For determining the position of the deflection state of the mechanical component, the laser beam reflected by the component is detected by photodetectors positioned in a suitable way. A disadvantage of the free beam arrangements is the needed large building space. Laser diodes and photodiodes as well as further optical components needed for beam shaping have to be arranged directly around the mechanical component. Further, in free beam arrangements trigger diodes are partially used as detectors. Trigger diodes only enable the execution of time-discrete measurements, using which no statistical deflections of the mechanical component can be determined. For the above-mentioned reasons, position sensors based on free beam arrangements are not suitable for being used in miniaturized systems, in particular for use in endoscopic applications.
A further category of position sensors includes integrated sensors for determining the deflection state of a movably arranged mechanical component. Capacitive position sensors contain capacitive structures suitably integrated into the component or connected to the component. A change of the deflection state of the mechanical component causes a measurable change in the electric capacity. Capacitive position sensors are, however, relatively inaccurate. Further, in micromechanics many components, like, e.g., microscanner mirrors, are driven electrostatically, so that it is difficult to separate the relatively high drive voltages sufficiently from the measurement signals. A sufficiently accurate determination of the position or the deflection state of a movably arranged mechanical component is not possible with capacitive position sensors.
Further, in microsystem technology, piezoresistive methods are known for determining the deflection state of a movably arranged mechanical component. For this method, however, there is also the problem of sufficiently separating the relatively high drive voltages from the measurement signals. The overlaying of the drive voltage with the measurement signals may be disadvantageous for the measurement resolution and thus for the determination of the position or the deflection state of the mechanical component.
Further, integrated capacitive and piezoresistive sensors need electronic circuits in the direct vicinity of the mechanical component for amplifying the measurement signals, as the unamplified measurement signals may not be transmitted over distances of any length. For this reason, position sensors based on integrated capacitive and piezoresistive sensors are not suitable for use in endoscopes which need small lateral dimensions and relatively long transmission distances of the measurement signals.